1. Field of the Invention
The present invention relates to an exciting method of magnetic field impressed on amorphous-alloy sensor, and especially an exciting method of magnetic field impressed on, such as, pressure sensor which uses an amorphous magnetic alloy as a sensing part.
2. Description of the Prior Art
Various kinds of sensor devices for detecting stress, strain and the like by utilizing magnetostriction of amorphous magnetic alloy, has been conventionally proposed. Principles of the detection are based on the following manner: Firstly, a magnetic circuit of the sensor is containing at least a part made by amorphous magnetic alloy. Secondly, a strain is generated on the amorphous magnetic alloy part at a measurement operation of an object, for example, strain of stress caused by pressure, tension, bending etc. Thirdly, detection of the change of magnetic characteristics of such magnetic circuit, especially, change of inductance of magnetic circuit is made. Fourthly, measuring of the value of the measurement object (such as stress, strain and the like) is made by the detected change of the magnetic characteristics. In order to detect the change or inductance of the magnetic circuit, a magnetic field generated by alternating current is given to the magnetic circuit. Hereupon, it is well known that the sensitivity of the sensor for detection may be raised, reproducibility can be improved, and thermal characteristics can be remarkably improved, by impressing such magnetic field that which is generated by alternating current superposed with direct current on the magnetic circuit. It becomes obvious that, however, the magnetic permeability of the amorphous magnetic alloy changes as time passes thereby deteriorating sensitivity and reliability of the measurement (this phenomenon is generally called as disaccommodation, and hereinafter abbreviated as disaccommodation). Accordingly, when using such amorphous magnetic alloy for a sensor device, a stable output can not be retained for long measuring time.
As mentioned above, the conventional method can not provide stable output because of the disaccommodation or amorphous magnetic alloy during long measuring, while the sensitivity of the conventional amorphous-alloy sensor is good. And therefore, an amorphous alloy sensor of long-time stable characteristic has been demanded.